In the area of display devices, flat panel devices are increasingly replacing Cathode Ray Tubes (CRTs) in many computer and television applications. Conventional flat panels, such as Liquid Crystal Displays (LCDs) and plasma displays are becoming cost effective for many applications. At present, LCDs are one of the most popular and mature technologies for low power and cost effective implementations.
Unfortunately, conventional LCDs do not have a wide viewing angle. In other words, when the viewing direction shifts away from perpendicular to the viewing screen, the light intensity and contrast perceived from the screen decreases. As a result, appearance of the image on the LCDs may change as the viewing angle changes. Recently, Photo-Luminescent LCDs (PL-LCDs) have been developed. PL-LCDs use a fluorescent screen, similar to that of CRTs, to generate color pixels. The various colors required to generate color pixels are formed by photo-luminescent compounds that generate a specific color wavelength when exposed to an excitation radiation. Conventionally, the excitation radiation may be ultraviolet light or deep blue light. An LCD panel modulates which pixels are exposed to the excitation radiation and which pixels are not exposed at any given time. The fluorescent screen eliminates much of the viewing angle problem while still allowing the use of LCD type panels to determine which pixels to excite. Various phosphors are well known for generating the red, green, and blue wavelengths needed to cover most of the visible light spectrum.
Raman Spectroscopy is a well-known spectroscopic technique for performing chemical analysis. In conventional Raman Spectroscopy, high intensity monochromatic light from a light source, such as a laser, is directed onto an analyte to be chemically analyzed. The analyte may contain a single species of molecules or mixtures of different molecules. Furthermore, Raman Spectroscopy may be performed on a number of different molecular configurations, such as organic and inorganic molecules in crystalline or amorphous states.
The majority of the incident photons of the light are elastically scattered by the analyte molecule. In other words, the scattered photons have the same frequency, and thus the same energy, as the photons that were incident on the analyte. However, a small fraction of the photons (i.e., 1 in 107 photons) are inelastically scattered by the analyte molecule at a different optical frequency than the incident photons. The inelastically scattered photons are termed the “Raman effect” and may be scattered at frequencies greater than, but most are usually scattered at a frequency lower than, the frequency of the incident photons. When the incident photons collide with the molecules and give up some of their energy, the Raman scattered photons (also referred to as Raman scattered radiation) emerge with a lower energy. The lower energy Raman scattered photons are commonly referred to in Raman spectroscopy as the “Stokes radiation.” A small fraction of the molecules are already in an energetically excited state and when the incident photons collide therewith, the Raman scattered photons emerge at a higher energy. The higher energy Raman scattered photons are commonly referred to in Raman spectroscopy as the “anti-Stokes radiation.” The Stokes and the anti-Stokes Raman scattered photons are detected by a detector, such as a photomultiplier, resulting in a spectral graph of intensity at a corresponding frequency (i.e., proportional to energy) for the Raman scattered photons. By plotting the frequency of the inelastically scattered Raman photons against intensity, a unique Raman spectrum, which corresponds to the particular analyte molecules, is obtained. This Raman spectrum may be used to identify chemical species, among other physical properties of the analyte. While conventional Raman Spectroscopy is suitable for bulk chemical analysis, it is not effective for surface studies because the signal from the bulk Raman scattered photons overwhelms any signal from Raman scattered photons near the surface.
Due to the deficiencies with performing surface studies using conventional Raman Spectroscopy, another Raman Spectroscopy technique called Surface Enhanced Raman Spectroscopy (SERS) which is effective for performing surface studies has been developed. In SERS, a monolayer of the molecules to be analyzed is adsorbed onto a specially roughened metal surface. Typically, the metal surface is made from gold, silver, copper, lithium, sodium, or potassium. SERS has also been used employing metallic nanoparticles or nanowires for the metal surface as opposed to a roughened metallic surface. The intensity of the Raman scattered photons from a molecule adsorbed on such a metal surface is typically about 104-106 greater than conventional Raman Spectroscopy and can be as high as 108-1014. Although not thoroughly understood, the selectivity of the surface Raman signal results from the presence of surface enhancement mechanisms and is mainly attributed to two primary mechanisms: electromagnetic enhancement and chemical enhancement, with the electromagnetic enhancement being the dominant mechanism. The enhanced electromagnetic field is highly dependent on the surface roughness features of the metal surface. The chemical enhancement is believed to be dependent on the altered electronic structure of the metal surface due to adsorbing the analyte. The enhanced electromagnetic field of the metallic surface, which is adjacent to the analyte, irradiates the analyte producing an enhanced Raman signal because the strength of the Raman signal is, in part, proportional to the square of the enhanced electromagnetic field. Thus, SERS may be used to study monolayers of materials adsorbed on metals.
Due to deficiencies in the conventional technology, a SERS analysis device combining a light amplifier and optical gating with a SERS analysis surface and analyte for performing SERS may generate a stronger radiation source, the intensity of which may be controlled by a modulated signal. Furthermore, a plurality of SERS analysis devices formed on a substrate may allow spatial analysis of an analyte. This spatial analysis may be combined with varying intensities at the various SERS analysis devices. In addition, a system incorporating a light amplifier and optical gating may be combined with photo-luminescent compounds to advantageously reduce power, reduce intensity of excitation radiation, and simplify system component design for display systems.